1. Field of the Invention
The present invention relates to a tape guide device adapted for use in a video tape recorder or the like and, more particularly, to a device where ultrasonic vibration is utilized to reduce the friction in contact with a tape.
2. Description of the Prior Art
There are known conventional tape guide devices inclusive of an example filed by the present applicant and disclosed in Japanese Patent Application No. Hei 1 (1989)-53287. As shown in FIG. 11, such known tape guide device 1 comprises a mount member 8, a pair of support shafts 7 fixed therein, a guide member 2 which is held by fore ends of the support shafts fitted into lateral portions thereof and serves to guide a tape wound therearound over a predetermined angle, and a laminated piezoelectric element 3 serving as an ultrasonic vibrator and bonded at one end to the guide member 2 while being bonded at the other end to the mount member 8. The guide member 2 is vibrated by standing waves from the laminated piezoelectric element 3 so as to diminish the resistance that is caused by agglutination derived from the intermolecular attraction and the interatomic attraction on the contact surfaces of the tape and the guide member 2 and also by thrust and upturn of the irregularities on such contact surfaces, hence reducing the frictional force.
FIG. 12 shows another conventional tape guide device proposed by the present applicant and disclosed in Japanese Patent Application No. Hei 1 (1989)-58449. The tape guide device of FIG. 12 is structurally similar to the aforementioned conventional example with the exception that a recess 2a is formed in a portion of the guide member 2, and both ends of the laminated piezoelectric element 3 are anchored firmly in such recess 2a.
However, in the former conventional example of FIG. 11, the respective thermal expansion coefficients of the support shaft 7 and the laminated piezoelectric element 3 are mutually different, so that there arises a problem of lowering the positional precision relative to the guide member 2. Furthermore, since one end of the laminated piezoelectric element 3 is fixedly attached to the guide member 2 as mentioned, the standing-wave frequency characteristic is harmfully affected by the vibrations of the mount member 8 and the support shafts 7 to be thereby complicated, hence rendering the resonance control difficult and lowering the vibration efficiency.
In addition, as the standing waves generated in the guide member 2 are affected by the mount member 8 and the support shafts 7, the partial standing waves thus affected are distorted to consequently fail in attaining complete reduction of the friction to the tape. Besides the above, the friction of the guide member is rendered partially nonuniform to eventually bring about a failure in stabilizing the motion of the tape.
Meanwhile in the latter conventional example of FIG. 12 where a recess 2a is formed in a portion of the guide member 2, both ends of the laminated piezoelectric element 3 are anchored firmly in such recess 2a, so that the harmful influence of vibration to other members can be reduced. However, since the guide member 2 is formed into an uncommon shape, it is extremely difficult to derive the resonance characteristic of the guide member 2, and the waveform of the standing waves is complicated similarly to the foregoing conventional example, hence raising the same problem. In addition, there also exist other problems inclusive of increased production cost that results from requirements of high precision relative to the component parts and the assembling with the process of cutting the recess 2a and so forth.
Furthermore, thermal expansion of the laminated piezoelectric element 3 is caused by the heat generated during the operation and therefore the surface secured to the recess 2a is pressed to consequently distort the guide member 2, hence failing in complete reduction of the friction while inducing harmful influence on the motion of the tape.